import java.util.Scanner;

public class Ex2_21{
	public static void main(String[] args){
		Scanner input = new Scanner(System.in);
		System.out.print("Enter three points for a triangle: ");
		double x1 = input.nextDouble();
		double y1 = input.nextDouble();
		double x2 = input.nextDouble();
		double y2 = input.nextDouble();
		double x3 = input.nextDouble();
		double y3 = input.nextDouble();
		double side1 = Math.pow((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1), 0.5);
		double side2 = Math.pow((x3-x1)*(x3-x1)+(y3-y1)*(y3-y1), 0.5);
		double side3 = Math.pow((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2), 0.5);
		double s = (side1 + side2 + side3) / 2;
		double area = Math.pow(s*(s-side1)*(s-side2)*(s-side3), 0.5);
		System.out.printf("The area of the triangle is %.1f\n", area);
	}
}
